func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, err error) {
	var ok bool
	if enginePtr, ok = dec.ignorerCache[wireId]; !ok {
		// To handle recursive types, mark this engine as underway before compiling.
		enginePtr = new(*decEngine)
		dec.ignorerCache[wireId] = enginePtr
		wire := dec.wireType[wireId]
		if wire != nil && wire.StructT != nil {